To impart a corrosion-resistant properties to the surface of substrates subject to corrosion, such as metals, typically, the surface is coated with chromium-containing compounds. However, chromium-containing compounds present concerns regarding adverse health and environmental effects. The use of electroactive organic polymers as corrosion-inhibiting coatings has been explored as a potential replacement for chromium-containing compounds. One such polymer is polyaniline which can be prepared by oxidative polymerization of inexpensive aniline and which has a relatively good solubility for solution-coating applications.
Polyaniline in its completely oxidized form is known as pernigraniline, and in its fully reduced form as leucoemeraldine. When there is an equal fraction of oxidized and reduced units in the polymer, it is referred to as emeraldine. Upon doping the emeraldine base with a protonic acid such as hydrochloric acid, the emeraldine base exhibits moderate electric conductivity of about 10 S/cm.
It has also been shown that the non-conductive base form of polyaniline as a coating on cold-rolled steel (CRS) offers good corrosion protection. Small amine compounds also have long been used as corrosion inhibitors.
Oligomeric aromatic amines with amino-terminated end groups are of interest in the polymer field due to their use as monomers for preparing polyamides, polyimides and epoxy polymers. The synthesis of amino-terminated oligomers via conventional routes, when possible, is often very complicated. n,nxe2x80x2-bis(4xe2x80x2-aminophenyl) -1,4-phenylenediamine, a reduced form of n,nxe2x80x2-bis(4xe2x80x2aminophenyl) -1,4-quinonenediimine, has been synthesized by catalytic hydrogenation of n,nxe2x80x2-bis (4xe2x80x2-nitrophenyl)-1,4-phenylenediamine and was used as a trimer of aniline in elucidating the structure-semiconductivity relationship of aniline oligomers. In addition, another method was developed for preparing this oligomer to use it as a building block for achieving a total unambiguous synthesis of polyaniline by way of Schiff base chemistry. Both of these methods involve multiple synthetic steps and reduction of the nitro groups in the precursors. As such, it is difficult to apply these methods generally for synthesizing polyaniline and its derivatives, or for using in industrial applications.
As described in U.S. Pat. No. 4,940,517 of Yen Wei, herein incorporated by reference, aniline polymerization is undertaken by using a small amount of an initiator additive, such as 1,4-phenylenediamine, 1,4-aminodiphenylamine, n,nxe2x80x2-diphenylhydrazine, benzidine and the like. These additives drastically increased the rate of the oxidative polymerization of the aniline monomers. The growth of polymer chains is achieved via electrophilic aromatic substitution on neutral monomers by the oxidized growing polymer chain ends. The polymerization process is neither a classical step nor a classical chain polymerization, but is more of a combination of these processes. The additives function as a chain initiator and the molecular weight of polyaniline can be modified by varying the amount of initiator.
The invention includes a method of forming an oligomer from monomers of Formula I: 
wherein R1 and R2 are independently selected from the group consisting of xe2x80x94H, xe2x80x94OH, xe2x80x94COOH, halogen, xe2x80x94NO2, xe2x80x94NH2, and substituted and unsubstituted alkyl, substituted and unsubstituted alkoxy and substituted and unsubstituted aryl groups; R1 substitutions being ortho or meta to the NHR2 group; and m is 0 to 4. The method comprises reacting the monomer of Formula (I), or a derivative or a water-soluble salt thereof, with greater than 10 mole percent of an initiator, in the presence of a chemical oxidant and/or an applied electrochemical potential. The initiator comprises a substituted or unsubstituted aromatic amine which has a lower oxidation potential than the monomer of Formula I and which is capable of being incorporated in a chain resulting from the reaction, wherein the oligomer has a molecular weight of less than 2300.
The invention also includes a method of forming an end-functionalized polymer from a monomer selected from the group consisting of compounds of Formula (III): 
wherein R3 is selected from the group consisting of xe2x80x94H, xe2x80x94OH, COOH, lower alkoxy, alkyl, aryl, halogen, xe2x80x94NO2, and xe2x80x94NH2, with substitutions being ortho or meta to the amine group; R4 is hydrogen or lower alkyl; and x is 0 to 4, derivatives of compounds of Formula (III), and salts of Formula (III). The method includes the steps of reacting the monomer with an initiator, in the presence of a chemical oxidant and/or an applied electrochemical potential to form a polymer. The initiator comprises a substituted or unsubstituted aromatic amine which has a lower oxidation potential than the monomer and which is capable of being incorporated in the polymer chain resulting from the polymerization reaction. The polymer is converted to its base form, and reacted in its base form with an organic aldehyde to form an end-functionalized polymer, wherein amine end groups of the polymer are converted to imine end groups in the end-functionalized polymer.
The invention additionally includes a method of forming a corrosion-resistant composition comprising a corrosion resistant copolymer, the method comprising copolymerizing a monomer and an oligomer selected from the group consisting of oligomers having the following formula: 
wherein X and Y are independently selected from the group consisting of H, xe2x80x94NH2, xe2x80x94C6H4NH2, xe2x80x94OC6H4NH2, alkyl, aryl, OH and OR5; R5 is selected from the group consisting of H, xe2x80x94OH, xe2x80x94COOH, alkyl, aryl, alkoxy, halogen, NO2 and xe2x80x94NH2; and n is from about 2 to about 40, derivatives of the oligomers of Formula (IV), salts of the oligomers of Formula (IV), and undoped or doped oligomers of Formula (IV) with Lewis or protonic acids, or fullerenes.
A method of forming a corrosion-resistant substrate is also within the invention. The method comprises coating at least one surface of the substrate with a composition comprising a corrosion-resistant oligomer selected from the group consisting of oligomers having the following formula: 
wherein X and Y are independently selected from the group consisting of H, xe2x80x94NH2, xe2x80x94C6H4NH2, xe2x80x94OC6H4NH2, alkyl, aryl, OH and OR5; R5 is selected from the group consisting of H,xe2x80x94OH, xe2x80x94COOH, alkyl, aryl, alkoxy, halogen, NO2 and xe2x80x94NH2; and n is from about 2 to about 400, derivatives of the oligomers of Formula (IV), and salts of the oligomers of Formula (IV).
The invention further includes a corrosion-resistant composition, comprising an oligomer selected from the group consisting of oligomers having the following formula: 
wherein X and Y are independently selected from the group consisting of H, xe2x80x94NH2, xe2x80x94C6H4NH2, xe2x80x94OC6H4NH2, alkyl, aryl, OH and OR5 ; R5 is selected from the group consisting of H, xe2x80x94OH, xe2x80x94COOH, alkyl, aryl, alkoxy, halogen, NO2 and xe2x80x94NH2 and n is from about 2 to about 400, derivatives of the oligomers of Formula (IV), and salts of the oligomers of Formula (IV).